EP3551943A1

EP3551943A1 - Hvac actuator

Info

Publication number: EP3551943A1
Application number: EP17828847.8A
Authority: EP
Inventors: Gaëtan MATTHEY; Silvio Grogg; Peter SCHMIDLIN
Original assignee: Belimo Holding AG
Current assignee: Belimo Holding AG
Priority date: 2016-12-08
Filing date: 2017-12-07
Publication date: 2019-10-16
Anticipated expiration: 2037-12-07
Also published as: US20200182506A1; CN110088538B; EP3551943B1; CN110088538A; WO2018104431A1; US11293662B2

Abstract

An HVAC actuator (1) comprises an electric motor (11); an energy buffer (13) configured to store electrical energy from a power supply (2), and to provide the electrical energy to the motor (11); and a power limiting circuit (12) configured to limit input power from the power supply (2) to the energy buffer (13) to a threshold lower than motor power drawn by the motor (11 ) from the energy buffer (13).

Description

HVAC ACTUATOR

Field of the invention

The present invention relates to an HVAC actuator, a system of HVAC actuators and a method of operating an HVAC actuator. Specifically, the present invention relates to an HVAC actuator, a system of HVAC actuators and a method of operating an HVAC actuator whereby the HVAC actuator comprises an electric motor.

Background of the invention

HVAC actuators comprising electric motors are commonly used to control HVAC devices, such as dampers or valves. The power consumed by the motor of the HVAC actuators is typically provided by mains supply which requires an adequate wiring of the HVAC actuators. Solutions using batteries or accumulators offer to some extent independency from external power supply, but often suffer from limited running time due to discharging processes or the considerable power consumption of the HVAC actuator. Further issues related to power supply may arise during installation of the HVAC actuators as the electrical wiring may not have been done and electrical power may initially not be available, and therefore, initial testing of the mechanical installation of the actuators in powered mode is not possible.

A power supply for a radiator thermostat using an energy storage and a thermoe- lectric energy converter for converting heat of a heating liquid into electrical energy is described in DE1 0201 31 1 0821 A1 . The thermoelectric energy converter is on one side coupled to the heating valve as a heat source and on another side coupled to a heat sink such as a housing of the radiator thermostat. The converted electrical energy is used for controlling and driving an electrical motor of a heating valve actuator. The energy storage includes, for example, an accumulator or a capacitor for receiving excess conversion energy.

DE 1 0201 0033428 A1 describes a controller for an actuator with a power supply, wherein the power supply includes an energy converter for converting energy from the surroundings into electrical energy. The power supply further includes an energy storage for storing the converted energy. The energy converter converts heat from the surroundings and relies on the Peltier orthe Seebeck effect. A temperature gradient usually present in the heating circuit can be used to apply such an energy conversion to a heating control. The energy converter can also convert mechanical oscillations, light, force electromagnetic fields etc. into electrical energy. The converted electrical energy is stored in an energy storage which can be an accumulator or a capacitor. As long as the energy storage is not fully loaded, the energy obtained from the energy converter is almost completely loaded into the energy storage.

The prior art describing power supplies with energy storage means have in common that an energy converter is foreseen for converting energy from the surroundings to electrical energy which is stored in the energy storage. Further, incoming energy is, whenever possible, fully extracted and loaded onto the energy storage in order to have the energy available for later application, without specific control of the power input to the HVAC actuator. Summary of the invention

It is an object of the invention to provide an HVAC actuator, a system of HVAC actuators and a method of operating an HVAC actuator, which at least partially improve the prior art and avoid at least part of the mentioned disadvantages of the prior art.

According to the present invention, this object is achieved by the features of the independent claims. In addition, further advantageous embodiments follow from the dependent claims and the description.

According to an aspect of the invention, the object is particularly achieved by an HVAC actuator, comprising an electric motor, wherein the HVAC actuator further comprises an energy buffer configured to store electrical energy from a power supply, and to provide the electrical energy to the motor. The HVAC actuator further comprises a power limiting circuit configured to limit input power from the power supply to the energy buffer to a threshold lower than motor power drawn by the motor from the energy buffer. The energy buffer has the advantage that an increased independency from the external power supply can be provided by storing electrical energy from the power supply in the energy buffer and controllably providing the electrical energy to the motor and/or further HVAC actuator components, when the energy is needed. The power limiting circuit has the advantage that input power can controllably be drawn from the power supply by limiting the input power to the threshold. Owing to the energy buffer configured to store electrical energy, the threshold can be set to be lower than motor power drawn by the electric motor from the energy buffer, such that an HVAC actuator with a lower input power demand can be provided. This has the advantage that smaller and, in particular, cheaper power supplies can be used. The threshold can initially be preset or be configurable in situ.

In an embodiment, the energy buffer is configured to accumulate and to store electrical energy during an idle time tidie of the motor and to provide electrical energy to the motor during an active time t_active of the motor. Typically, the HVAC devices, such as damper blades, valves etc., do not change their position or state (e.g. open/closed) continuously, but remain in a certain position between changing the position, such that motors of HVAC actuators driving the HVAC devices can stay idle when the position of the HVAC device is kept constant. During the idle time tidie, power for changing the actuator position is therefore not required and typically only residual power is consumed by the electronics of the HVAC actuator, for example by a motor controller. In an embodiment, the energy buffer accumulates and stores electrical energy only during the idle time tidie- Optionally, the energy buffer can accumulate and store the electrical energy also during the active time t_active of the motor.

In an embodiment, the power limiting circuit is configured to set the threshold such that the electrical energy stored in the energy buffer during the idle time t_idi_e is sufficient to drive the motor during the active time t_active- Typically, motors of HVAC actuators exhibit active times which are shorter than idle times, due to the typical situation that the HVAC devices driven by the HVAC actuators remain in a certain position most of the time and the position of the HVAC devices is usually changed intermittently.

In an embodiment, the HVAC actuator further comprises a motor controller configured to monitor an operating condition of the energy buffer. The motor controller is further configured to store a safety position and to drive the motor to the safety position, depending on the operating condition of the energy buffer, using electrical energy stored in the energy buffer. The operating condition of the energy buffer can be based at least on one of, for example, voltage, charge, energy, power of the energy buffer indicating the performance and /or ageing of the energy buffer. For the case that the operating condition monitored by the motor controller indicates that the performance of the energy buffer has been degraded, the motor controller may drive the motor to the safety position, such that accidental driving into an erroneous position of the motor due to a low performance of the energy buffer can be avoided.

In an embodiment, the power limiting circuit is configured to set the threshold such that the electrical energy stored in the energy buffer is sufficient to feed the motor controller.

Optionally, the HVAC actuator further comprises at least one sensor, for example for variable air volume (VAV) control, temperature control, humidity control etc. Advantageously, the power limiting circuit may be configured to set the threshold such that the electrical energy stored in the energy buffer is sufficient to feed the at least one sensor. In an embodiment, the HVAC actuator further comprises a regulator configured to convert input voltage of the HVAC actuator to a voltage lying in a voltage range of the energy buffer.

In an embodiment, the regulator is a switching regulator. In an embodiment, the power limiting circuit is configured to adjust the threshold depending on a conversion efficiency regulator of the regulator. This has the advantage that the power limiting circuit can adjust the threshold to compensate power loss by the regulator and to maintain sufficient power output from the regulator to the energy buffer. In an embodiment, the power limiting circuit and the regulator are integrated in a single power limiting unit.

For the case of zero input power to the HVAC actuator, the energy buffer may be configured to operate in a battery mode for driving the motor during a time tbatt. The energy buffer running in a battery mode is understood as the energy buffer being able to provide electrical energy for a duration of time tbatt, without being connected to an external power supply.

In an embodiment, the energy buffer is a Lithium-ion capacitor. Lithium-ion capacitors have the advantage of high energy densities yielding low space requirements inside the HVAC actuators and low self-discharge rates offering high reliability, es- pecially for running in battery mode. In an embodiment, the HVAC actuator further comprises an activation switch configured to activate the HVAC actuator, from a deactivated, energy conserving state to an active state, for the case of zero input power to the HVAC actuator.

According to a further aspect, the present invention is also directed to a system comprising a plurality of HVAC actuators according to the present invention, connected to a common power supply line, wherein the power supply line provides input power to the HVAC actuators, the input power in each case being limited by the power limiting circuits of the HVAC actuators. The system comprising a plurality of HVAC actuators with power limiting circuits has the advantage of increased controllability in distribution of power of the common power supply line to the plurality of the HVAC actuators.

In an embodiment, the power limiting circuits of the HVAC actuators are configured to adjust the thresholds depending on the number of HVAC actuators connected to the common power supply line. This has the advantage that the system can adapt to the actual number of HVAC actuators connected to the power supply line, for example, if an additional HVAC actuator is additionally coupled to the power supply line or if an HVAC actuator is removed from the power supply line. Thereby, a risk of overloading the power supply line can be avoided, if, for example, additional HVAC actuators are coupled to the power supply line. Accordingly, an optimal load of the power supply line can be ensured, if, for example, some HVAC actuators are removed from the power supply line. In an embodiment, the power limiting circuits of the HVAC actuators are configured to adjust the thresholds depending on the power of the common power supply line. This has the advantage that the system can adapt to characteristics of the common power supply line, for example the maximum power that can be delivered by the power supply line, which may be considerably lower than the motor power drawn by each of the HVAC actuators.

In an embodiment, the common power supply line comprises a power over Ethernet line.

According to a further aspect, the present invention is also directed to a method of operating an HVAC actuator comprising an electric motor, whereby the method comprises: storing electrical energy from a power supply in an energy buffer of the HVAC actuator and providing the electrical energy to the motor; limiting by a power limiting circuit of the HVAC actuator input power from the power supply to the energy buffer to a threshold lower than motor power drawn by the motor from the energy buffer.

In an embodiment of the method, the energy buffer is loaded with an initial energy sufficient to drive the actuator in battery mode for a predetermined time t prior to initial operation of the HVAC actuator.

According to a further aspect, the present invention is directed to an HVAC actuator comprising an electric motor, the HVAC actuator further comprising an energy buffer configured to store electrical energy from a power supply, and to provide the electrical energy to the motor, wherein the HVAC actuator further comprises an activation switch configured to activate the HVAC actuator, from a deactivated, energy conserving state to an active state, for the case of zero input power to the HVAC actuator. The activation switch is particularly advantageous for initial operation of the HVAC actuator, for example at installation time, when an external power supply is not yet available or connected. When the HVAC actuator is stored prior to first use, the HVAC actuator is set in the deactivated state, completely shut down, in order to prevent or to at least minimize discharge of preloaded initial energy of the energy buffer during storage.

As a particular advantage, the activation switch makes it possible to set the HVAC actuator in active state, activating the HVAC actuator for operation in battery mode. After initial operation during a time tbatt, which may include tasks such as, for example, actuator adaptation by driving the HVAC actuator to its maximal angular positions, the activation switch can be used for re-shutting down the HVAC actuator, setting the HVAC actuator into the deactivated, energy conserving state.

In an embodiment, the activation switch is configured to activate the HVAC actuator only for at least a time tbatt for initial operation, after which the HVAC actuator returns to the deactivated, energy conserving state.

In an embodiment, the activation switch comprises a manual switch for manual activation. In an embodiment, the HVAC actuator further comprises a near field communication (NFC) module configured to activate the HVAC actuator, from a deactivated, energy conserving state to an active state. The NFC module may be connected to the activation switch. The NFC module has the advantage of enabling a contactless activation of the HVAC actuator. Further, the NFC module may be used for information exchange for selecting initial operation tasks.

Brief Description of the Drawings

The present invention will be explained in more detail, by way of example, with reference to the drawings in which:

Figure 1 : shows a block diagram illustrating schematically an embodiment of an

HVAC actuator comprising an energy buffer and a power limiting circuit;

Figure 2: shows a block diagram illustrating schematically an embodiment of a system comprising a plurality of HVAC actuators.

Detailed Description of the Preferred Embodiments

Figure 1 shows a block diagram of an embodiment of an HVAC actuator 1 which receives electrical power from an external power supply 2 via a wire connection. The HVAC actuator 1 comprises an electric motor 1 1 , which is used to drive an HVAC device such as a damper or a valve, etc. The input power from the power supply 2 is limited by a power limiting circuit 1 2 to a threshold P_th. The threshold P_th may be configurable by the power limiting circuit 1 2. The power limiting circuit 1 2 can comprise shunt elements and/or control circuitry. The power limited by the power limiting circuit 1 2 is fed to a regulator 1 4, which regulates supply voltage of the power supply 2, typically 24 V, to a voltage in a range of an energy buffer 1 3, which is arranged downstream of the regulator 1 4. Preferably, the regulator 14 is a switching regulator, which offers high efficiency, low power dissipation and high power density. The high power density of the switching regulator has the advantage that space requirements can be kept small inside the HVAC actuator 1 . The efficiency Ή regulator of the switching regulator can be as high as 80 % or higher. The threshold P_th is lower than the electrical motor power P_motor drawn by the motor 1 1 from the energy buffer 1 3 arranged in the HVAC actuator 1 . The threshold P_th can be adjusted depending on various circumstances, for example depending on the motor power Pmotor, on the power supplied by the power supply 2, etc. The energy buffer 1 3 is arranged downstream of the power limiting circuit 1 2 and is configured to store electrical energy from the power supply 2 and to provide the stored electrical energy to the motor 1 1 . Typically, the motor 1 1 of the HVAC actuator 1 is driving the HVAC device during an active time t_active. During the rest of the time t_id!e, the HVAC device stays idle and typically only residual power is consumed by the electronics of the HVAC actuator 1 , for example by a motor controller 1 5. Therefore, the energy buffer 1 3 has to provide electrical energy to the motor 1 1 for changing the actuator position during the active time tactive- During the idle time tdie, and optionally also during the active time tactive, the energy buffer 1 3 accumulates and stores electrical energy.

In an embodiment, the power limiting circuit 1 2 and the regulator 1 4 are integrated in a single power limiting unit 1 0, as symbolized by the dashed box. The regulator 1 4 outputs an electrical loading power Pi_oad which is related to the threshold P_th as follows:

Pioad ~ regulatorPth

The loading power Pi_oad is used to load the energy buffer 1 3 at least during the idle time tidie, such that the electrical energy accumulated and stored at least during the idle time tidie is sufficient for the energy consumption of the motor 1 1 during the active time t_active. Further, the electrical energy accumulated and stored at least during the idle time tidie is sufficient for the residual power consumption of the electronics of the HVAC actuator 1 . The loading power Pi_oad therefore satisfies the following relation:

_D ^-active„

' load — ~1 ' motor

Hdle

As an example, the motor 1 1 exhibits a maximum motor current of 60 mA at a voltage of 3.3 V, such that the motor power is 200 mW. Assuming that the motor 1 1 drives an HVAC device during an active time t_active which is half of the idle time tidie, the loading power Pi_oad should at least be 1 00 mW. Together with the motor voltage of 3.3 V this yields a loading current of 30 mA during the idle time tidie- With an efficiency r|regui_ator of the regulator 1 4 of 80%, the configurable threshold P_th to the input power is adjusted to ca. 1 25 mW in order to achieve the loading power ■ load of ca. 1 00 mW. The energy buffer 1 3 is preferably a Lithium-ion capacitor ( LIC), which has the advantage of a high energy density and a low self-discharge rate. The voltage range is typically between 2 V and 3.5 V, which advantageously corresponds to the range of the motor electronics. Especially, using a motor controller 1 5 with a voltage range corresponding to the voltage range of the energy buffer 1 3 , no up-conver- sion is necessary, which reduces the costs and the space required in the HVAC actuator 1 .

In the embodiment shown in Fig.1 , the HVAC actuator 1 further comprises a motor controller 1 5. The motor controller 1 5 may comprise a microcontroller. In an embodiment, the motor controller 1 5 comprises a motor driver IC. The energy buffer 1 3 provides electrical energy to the motor controller 1 5. The motor controller 1 5 drives the motor 1 1 and draws the motor power from the energy buffer 1 3. Accordingly, the loading power Pi_oad satisfies the following relationship

p _> ^active _(p p

¹ load — . \^rmotor ' ^r control⁾

Hdle such that the energy buffer 1 3 stores sufficient energy at least in the idle time ¾ι_ε, that can be provided to the motor 1 1 and the motor controller 1 5 during the active ti me tactive.

The motor controller 1 5 is configured to monitor an operating condition of the energy buffer 1 3, which is symbolized by the double arrow d. Depending on the operating condition of the energy buffer 1 3, the motor controller 1 5 can prompt the motor 1 1 to drive to a safety position which is stored in the motor controller 1 5. This can for example be the case, if the motor controller 1 5 monitors the ageing of the energy buffer 1 3 based on, for example, the discharge rate, maximum stored energy etc., and detects that the performance of the energy buffer 1 3 has considerably degraded, in that case, the motor controller 1 5 controls the motor 1 1 , respectively, to move to or drive an actuated part to a safety position, such that an accidental moving or driving to an erroneous position, due to a poor performance of the energy buffer 1 3, can be avoided. For obtaining the safety position, the energy buffer 1 3 is configured to provide the electrical energy to drive the motor 1 1 to the safety position. For example, the energy buffer 1 3 comprises a separate safety storage where the electrical energy, required for one-time driving the motor 1 1 into the safety position, is stored.

In an embodiment, the HVAC actuator 1 comprises a communication unit (not shown in Fig. 1 ), which can be used to send out a signal to an external maintenance site or an indication unit which indicates the condition of the energy buffer 1 3, such that a maintenance of the HVAC actuator 1 can be initiated when the safety posi^¬ tion is taken by the motor 1 1 . In an embodiment, the condition of the energy buffer 1 3 can be monitored by a separate diagnose unit (not shown in Fig. 1 ).

The HVAC actuator 1 further comprises a control interface 1 7 which receives an external control input symbolized by the arrow c. The control interface 1 7 transfers the external control input to the motor controller 1 5. Depending on the embodiment, the control interface 1 7 is an analogue or digital control interface. For example, the control interface 1 7 is based on a conventional interface for HVAC actuators, such as multi-point (M P), building automation and control network (BACnet), Modbus etc. In a variant, the control interface 1 7 includes a wireless network interface. In some embodiments, the control interface 1 7 includes an analogue interface with a control signal or operating range between 0 to 1 0 V or 2 to 1 0 V, such as for example used for spring-return actuators.

During first time installation of the HVAC actuator 1 , there is typically no power supply connected to the HVAC actuator 1 . The input power is therefore zero. Conventionally, the person installing the HVAC actuator 1 manually drives the HVAC device into the desired starting position (for example a certain open and /or closed position for dampers or for valves), for example by using a hand wheel. Especially for HVAC actuators installed in positions difficult to access, this can be cumbersome.

The energy buffer 1 3, especially in embodiments where the energy buffer is a LIC, can operate in a battery mode for driving the motor 1 1 during a time tbatt, during which the HVAC actuator is not connected to an external power supply. In an embodiment, the energy buffer 1 3 is loaded prior to first use with an initial energy sufficient to drive the motor 1 1 in battery mode. Therefore, a manual driving of the HVAC device into the desired starting position can be avoided at installation since the energy buffer 1 3 is able to provide the required initial energy. Prior to first use, the HVAC actuator 1 is preferably completely shut down, i.e. set in a deactivated, energy conserving state, in order to prevent or at least minimize discharge of the loaded energy buffer 1 3 during storage of the HVAC actuator 1 , e.g. unused in a box. At installation time, the completely shut down HVAC actuator 1 can be activated by an activation switch (not shown in the Figures), which may comprise a manual switch (e.g. a button) or be connected to an N FC module and is configured to place the HVAC actuator 1 from the deactivated, energy conserving state to an active state where the HVAC actuator 1 is powered by the energy buffer 1 3 in the case of zero input power. For example, in the deactivated state, the motor 1 1 is electrically disconnected from the energy buffer 1 3 by the switch.

Figure 2 shows a block diagram of an embodiment of a system 3 comprising a plurality of HVAC actuators 1 a, 1 b, 1 c,..., 1 n,... coupled to a common power supply line 4, which supplies input power to the HVAC actuators 1 a, 1 b, 1 c,..., 1 n,... The dotted line between the HVAC actuator 1 c and 1 n and after the HVAC actuator 1 n symbolizes further HVAC actuators, which are coupled to the same common power supply line 4, but are for simplicity not shown in Fig. 2. The HVAC actuator 1 a comprises a power limiting circuit 1 2a, an energy buffer 1 3a, and an electric motor 1 1 a. The respective power limiting circuits 1 2b, 1 2c, 1 2n, energy buffers 1 3b, 1 3c, 1 3n and electric motors 1 1 b, 1 1 c, 1 1 n are shown for the HVAC actuators 1 b, 1 c and 1 n. The power limiting circuits 1 2a, 1 2b, 1 2c,..., 1 2n,... of the HVAC actuators 1 a, 1 b, 1 c,..., 1 n,... limit input power from the common power supply line 4 to the energy buffer 1 3a, 1 3b, 1 3c,..., 1 3n,... to a threshold P_th lower than motor power drawn by the motors 1 1 a, 1 1 b, 1 1 c,..., 1 1 n,... from the energy buffers 1 3a, 1 3b, 1 3c,..., 1 3n,... Typically, the threshold P_th is the same for all HVAC actuators 1 a, 1 b, 1 c,..., 1 n. In some embodiments, the thresholds P_th may vary from HVAC actuator to HVAC actuator 1 a, 1 b, 1 c,..., 1 n, depending on the specific application. The energy buffers 1 3a, 1 3b, 1 3c,..., 1 3n,... accumulate and store electrical energy, and provide the electrical energy to the motors 1 1 a, 1 1 b, 1 1 c,..., 1 1 n,.... The shown system 3, comprising a plurality of HVAC actuators 1 a, 1 b, 1 c,..., 1 n,... with power limiting circuits 1 2a, 1 2b, 1 2c,..., 1 2n,..., has the advantage that the power P of the common power supply line 4 can controllably be distributed to the plurality of HVAC actuators 1 a, 1 b, 1 c,..., 1 n,... coupled to the common power sup- ply line 4. This is particularly advantageous, if the common power supply line 4 provides a power which is lower than the motor power drawn by the motors 1 1 a, 1 1 b, 1 1 c,..., 1 1 n,... from the energy buffers 1 3a, 1 3b, 1 3c,..., 1 3n,... , which is for example the case for an embodiment where the common power supply line comprises a Power over Ethernet (PoE) line. Especially, the power of the common power supply line 4 may be sufficient to supply one or a certain number ni of HVAC actuators, but may not be sufficient, if a number n₂>m of HVAC actuators are coupled to the common power supply line 4. By limiting the input power for each HVAC actuator, the system can operate even for the n₂ HVAC actuators, without the power supply line 4 being overloaded. For the case of n HVAC actuators coupled to the common power supply line 4, the threshold P_th may be set to P/n, such that an overload of the common power supply line 4 can controllably be avoided. Accordingly, the level of power required from the power supply line can be reduced, since the input power is limited by the power limiting circuits and distributed to the plurality of HVAC actuators. The limited input power P/n per HVAC actuator can be accumulated and stored in the respective energy buffers 1 3a, 1 3b, 1 3c,..., 1 3n,... at least during the idle time t,die of the motors 1 1 a, 1 1 b, 1 1 c, ....1 1 n,... and provided to the motors 1 1 a, 1 1 b, 1 1 c,..., 1 1 n,... during the active time t_active. In an embodiment, the HVAC actuators 1 a, 1 b, 1 c,..., 1 n,... are centrally controllable using control interfaces (not shown in Fig.2), such that the thresholds P_th can centrally be adjusted. This has for example the advantage that the thresholds P_th can be readjusted, if one of the HVAC actuators fails (for example after the motor being driven to a safety position) or if an additional HVAC actuator is coupled to the common power supply line 4.

Claims

An HVAC actuator ( 1 , 1 a, 1 b, 1 c, 1 n), comprising an electric motor ( 11 , 11 a, 11 b, 11c, 11 n), wherein the HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) further comprises: an energy buffer (13, 13a, 13b, 13c, 13n) configured to store electrical energy from a power supply (2, 4), and to provide the electrical energy to the motor (11, 11a, 11b, 11c, 11n);and a power limiting circuit (12, 12a, 12b, 12c, 12n) configured to limit input power from the power supply (2, 4) to the energy buffer (13, 13a, 13b, 13c, 13n) to a threshold lower than motor power drawn by the motor (11, 11a, 11b, 11c, 11 n) from the energy buffer ( 13, 13a, 13b, 13c, 13n).

The HVAC actuator (1, 1a, 1b, 1c, 1n) according to claim 1, wherein the energy buffer (13, 13a, 13b, 13c, 13n) is configured to accumulate and to store electrical energy during an idle time t_iciie of the motor (11 , 11a, 11 b, 11c, 11 n) and to provide electrical energy to the motor (11, 11a, 11b, 11c, 11 n) during an active time t_active of the motor ( 11 , 11 a, 11 b, 11 c, 11 n).

The HVAC actuator ( 1 , 1 a, 1 b, 1 c, 1 n) according to claim 2, wherein the power limiting circuit (12, 12a, 12b, 12c, 12n) is configured to set the threshold suchthatthe electrical energy stored in the energy buffer (13, 13a, 13b, 13c, 13n) during the idle time tdie is sufficient to drive the motor (11, 11a, 11b, 11c, 11 n) during the active time t_active-

4. The HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) according to one of claims 1 to 3, wherein the HVAC actuator (1, 1a, 1b, 1c, 1 n) further comprises a motor controller (15) configured to monitor an operating condition of the energy buffer (13, 13a, 13b, 13c, 13n), to store a safety position, and to drive the motor (11, 11a, 11b, 11c, 11 n) to the safety position depending on the operating condition of the energy buffer (13, 13a, 13b, 13c, 13n), using electrical energy stored in the energy buffer (13, 13a, 13b, 13c, 13n).

5. The HVAC actuator ( 1 , 1 a, 1 b, 1 c, 1 n) according to claim 4, wherein the power limiting circuit (12, 12a, 12b, 12c, 12n) is configured to set the threshold such that the electrical energy stored in the energy buffer (13, 13a, 13b, 13c, 13n) is sufficient to feed the motor controller (15).

6. The HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) according to one of claims 1 to 5, further comprising a regulator ( 14) configured to convert input voltage of the HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) to a voltage lying in a voltage range of the energy buffer (13, 13a, 13b, 13c, 13n).

7. The HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) according to claim 6, wherein the regulator ( 14) is a switching regulator.

8. The HVAC actuator ( 1 , 1 a, 1 b, 1 c, 1 n) according to claim 6 or 7, wherein the power limiting circuit (12, 12a, 12b, 12c, 12n) is configured to adjust the threshold depending on a conversion efficiency η regulator of the regulator (14).

9. The HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) according to one of claims 1 to 8, wherein for thecaseof zero input power to the HVAC actuator (1, 1a, 1b, 1c, 1 n), the energy buffer ( 13, 13a, 13b, 13c, 13n) is configured to operate in a battery mode for driving the motor ( 11 , 11 a, 11 b, 11 c, 11 n) during a time tb_att.

10. The HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) according to one of claims 1 to 9, wherein the energy buffer ( 13, 13a, 13b, 13c, 13n) is a Lithium-ion capacitor.

11. The HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) according to one of claims 1 to 10, wherein the HVAC actuator (1, 1a, 1b, 1c, 1n) further comprises an activation switch con- figuredto activate the HVAC actuator (1, 1a, 1b, 1c, 1n), from a deactivated, energy conserving state to an active state, for the case of zero input power to the HVAC actuator (1, 1a, 1b, 1c, 1n).

12. The HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) according to one of claims 1 to 11 , wherein the HVAC actuator ( 1 , 1a, 1b, 1c, 1n) further comprises a near field communication module configured to activate the HVAC actuator ( 1 , 1a, 1b, 1c, 1 n), from a deactivated, energy conserving state to an active state.

13. A system (3) comprising a plurality of HVAC actuators (1a, 1 b, 1c, 1 n) according to one of claims 1 to 12, connected to a common power supply line (4), wherein the power supply line (4) provides input power to the HVAC actuators (1a, 1b, 1c, 1n), the input power in each case being limited by the power limiting circuits ( 12a, 12b, 12c, 12n) of the HVAC actuators (1a, 1b, 1c, 1n).

14. Thesystem (3) according to claim 13, wherein the power limiting circuits (12a, 12b, 12c, 12n) of the HVAC actuators (1a, 1b, 1c, 1n) are configured to adjust the thresholds depending on the number of HVAC actuators (1a, 1b, 1c, 1 n) connected to the common power supply line (4).

15. The system (3) according to claim 13 or 14, wherein the power limiting circuits ( 12a, 12b, 12c, 12n) of the HVAC actuators (1a, 1b, 1c, 1n) are configured to adjust the thresholds depending on the power of the common power supply line (4).

16. The system (3) according to one of claims 13 to 15, wherein the common power supply line (4) comprises a power over Ethernet line.

17. A method of operating an HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) comprising an electric motor ( 11 , 11 a, 11 b, 11 c, 11 n), the method comprising: storing electrical energy from a power supply (2, 4) in an energy buffer (13, 13a, 13b, 13c, 13n) of the HVAC actuator (1 , 1a, 1b, 1c, 1 n) and providing the electrical energy to the motor (11 , 11 a, 11 b, 11 c, 11 n); and limiting by a power limiting circuit (12, 12a, 12b, 12c, 12n) of the HVAC actuator ( 1 , 1a, 1b, 1c, 1 n) input power from the power supply (2, 4) to the energy buffer (13, 13a, 13b, 13c, 13n) to a threshold lower than motor power drawn by the motor (11, 11a, 11b, 11c, 11n) from the energy buffer (13, 13a, 13b, 13c, 13n).